Building a computer with discrete transistors

You’re going to want to do some stretching before undertaking a soldering project like this one. We’re betting that the physical toll of assembling this 4-bit discrete processor project is starting to drive [SV3ORA] just a bit crazy. This small piece of electronic real estate is playing host to 62 transistors so far, and he’s not done yet.

It’s one thing to build some logic gates in Minecraft (and then turn then into a huge 16-bit ALU). But it’s another thing to actually commit to a physical build. [SV3ORA] does a great job of showing the scope of the project by posting a tight shot of one inverter, then three in a row, then the entire 8-bit address and display system. These gates are built on the copper side of the board, with the power feed, LEDs for displays, and jumpers for control on the opposite side. We’re excited to see where he goes with this project!

Bonus points: Put LEDs on all gates and run it in single-step mode or at a low speed. A visual tool for instructors! Visual simulators on a PC is possible too but… just isn’t quite as good as an in-your-face circuit board that you can pick up and play with.

Hello there!
It all started by finding the Galactic electronics 4-bit CPU. It was so easy to understand how it worked, that I could not resist to build one. I am already building one with TTL like the author, BUT I am building the RAM as well as the EPROM using TTL as well. Now, that is a huge project already, if you realize that just the decoder for the ram takes 17 74ls154 to be made. I have not seen any homebrewer do it this way, they all seem to stick with out of the box RAM chips, because these are complex indeed.
Now imagine how this can be done transistorized, really this is huge! I do not think I will have the patience to make a 256 positions RAM, I think I will go for something like 32 or 64, but I will see how it goes.
But the resto of the computer is not really too tough. Some circuits, for example the clock, could be replaced by simpler ones (like a simple transistor multivibrator). Also for the EPROM, a diode matrix aproach could possibly be done.
I am glad you have fun seeing this project eventhough it is less than 1/20 finished :)